Process for producing magnetic manganese-zinc ferrite with isoperm character



Feb. 2, 1965 E. MOSER ETAL 3,168,476

PROCESS FOR PRODUCING MAGNETIC MANGANESE-ZINC FERRITE WITH ISOFERM CHARACTER Filed Feb. 3, 1961 s Sheets-Sheet 1 Fig.1 B

Feb. 2, 1965 E. MOSER ETAL 3,168,476

PROCESS FOR PRODUCING MAGNETIC MANGANESE ZINC 1 FERRITE WITH ISOPERM CHARACTER Filed Feb. 5, 1961 3 Sheets- Sheet 2 Feb. 2, 1965 E. MOSER ETAL 3,163,476

PROCESS FOR PRODUCING MAGNETIC MANGANESEZINC FERRITE WITH ISOFERM CHARACTER Filed Feb. 5, 1961 3 Sheets-Sheet 3 1.0 A/cm o l- 1 H c o a (D geous.

United States Patent M This invention is. concerned with a method of producing a,soft magnetic .ferrite withisoperm character.

The isoperm character is realized in connection with magnetic materials the hysteresis loop of which has, in addition to a relatively low remanence induction and corcive power, as. far reachingas possible a linear parallelism of the inclined branches of: the hysteresis loop. The

1 term isoperm character is intended to mean that the hysteresis loop is in its middle part described by an obliquely extendingparallelogram the width of which corresponds to twice the coercive powenii and the height of which corresponds at least to twice the remanence induction B The remanence induction shall amount to less than about 25 percent of the saturation induction B Theproperties of such isoperm magnetic materials are for many instances of use extraordinarily advanta- Such magnetic materials offer as compared with magnetic materials with normal hysteresis loop great advantages, particularly as core materialsfforjhighgrade filter coils.

The isoperm ferrites according to the invention show, in addition to the. general advantages .offerrites so far as eddy current losses and high initial permeability are concerned, low remanence and with increasing field strength only slight increase of permeability up to maximum permeability. The hysteresis losses are moreover .very low. .The'alignment error of the reversible permeability is likewise slight. Moreover, the initial permeability is with ferrites according to the invention very constant as to time and relatively insensitive totemporary magnetic or thermal loads.

, The ferrites produced according to the invention are very densely sintered, so that the isoperm-like hysteresis loop obviously cannot be traced to a shearing of the ferrite which would produce unfavorable and, of course, un-

desired properties. The ferrites according to the inventiondo not require, any treatmentin a magnetic'field.

There are ferrites knownjwith an isoperm loop, which areproducedby particular magnetic field treatment from socalled lerminvar ferrites.

..c'ent by weight silicic acid and at the most respectively about 0.03 percent by weight of other disturbing substances, wherein the amounts of the ferrite-forming initial substances are determined by a mixing area in the three substance iron-manganese-zinc diagram, suc'hj mixing area being described by the corner points, namely (1) 50 mole percent Fe O 24 mole percent MnO,

26 mole percent ZnO;

52 mole percent Fe O 16 mole percent MnO,

32 mole percent ZnO; and

thereupon dried and preannealed at a temperature- ,tween 850 C. and 950 C preferably atj900-C.,

Patented Feb. 2, 1965 (3) 57.5 mole percent Fe o 42.5 mole percent MnO.

These initial substances are intermixed and pre ferably annealed prior to'th'e'final sintering'thereof. frne sintered ferrite body is cooledin aninert gasa'trriosplie ample, in nitrogen.

Disturbing substances are particularly those elements the ion radii of which are greaterthanwthe ion radius of the largest element partaking in the "buildingup of the ferrite grid, in the present case,the manganese.

()f particular interestin the rangeotflthethree substance diagram determined by the'inven ti on is the region with less than 24 mole percent -MnO. Particularly high initial permeabilities up to ,u =7000 can be reached in this region. The region with less *than" lounole -percent ZnO is distinguished by high Curie'temperatures (T above 250 C. and high valtiesof-"the saturat ion magnetization in the produced ferrite which are only slightlyi dependent upon the temperature. i Q i i V The oxides composed according to the invention. from the region of the three Substance diagram are mixed wet for about ,six hours, fonexampl inaro cker ill,

t'nereaiter again subjected to wet grinding for,about two hours. Cores are now formed from the resulting powder by pressure molding and such cores are sinteredflin air, nitrogen oran air-nitrogen mixture or first'in air and thereafter in nitrogen, at temperatures between 1240" C. and 1350" C. for one to fifteenhours, preferably for two hours, whereupon they are cooled in an inert-gasfatmosphere, for example, in pure nitrogen. In accordance with the invention, the formation of the isoperm eharacter is favored by rapid cooling from the sinter temperature to I a temperature from 9005C. to 500 O-within-aninterval from five to fif teen minutes. Such-rapid coolingis particularly indicated in the case of, coresthe dimensions of which are'at least in one. direction very small,--for example ring cores with athic kness'of onlyonemillimeter or less.

s The ferrites produced according to the. invention thaye initial permeabilities from about a ZOOOtbJOOtL-relative temporal inconstancy values -i smaller than 5.10 and incidental reference hysteresis value 71/zi smaller than 0510-? cm./ka.; whereirf'h ,is" Jordans incide'ntal hysteresis value (see, for example, M. Kornetzki, Zeitschr'ift fiir an'gewandte 'Physilg; 4.11952) pages 343 to 345 and 6 (1954), pages 547 to 5 50 ),:-and.i being the relative variation?0 f-'the-initia1 permeability in the time interval from one to ten hour after passingternperature increase to 1;50 C. F'The reversibleepermeability at the remanence point :lies aboutl-O percent below the initial permeability. The density :of g the coresv amounts to about 4.6 to'4.8 g./cm. The isoperm character is less pronounced whenithe cores areproducedfiwithout the preannealing of the oxidemixture.

Some examples will now be given concerning the production of isoperm ferrites accordingto the invention.

Example 1 i Composition:

53.5 mole percent Fe O 30.5 mole percent MnO, and

16.0 mole percentZn'O."

The oxides which are constituted so that the total impurities in the end product amount to lessthani0.2 .percent by weight, arewith the additionof water in an amount of three times that of the oxides, intermixed by ther with an addition of a binder agent, for two hours, whereupon rings are pressure molded therefrom. which are sintered for one hour in nitrogen at 1280 C. The rings have an outer diameter of 20 millimeters and a thickness of 6 millimeters. The cooling from the sinter temperature to normal temperature is effected within twelve hours in pure nitrogen with an oxygen content of less than 0.02 percent by volume. The ferrites exhibited the following characteristic magnetic values:

wherein ,u =maximum permeability, B =magnetization at 1,0 a./cm., B =remanent magnetization.

Example 2 Composition:

52.4 mole percent Fe O 25.4 mole percent MnO, and 22.2 percent mole ZnO.

Cores formed as described in the first example, are sintered at 1320 C. for two hours in nitrogen containing 7 percent by volume oxygen, and thereupon rapidly cooled to 850 C., within ten minutes, in nitrogen containing 0.2 percent by volume oxygen. The further cooling to room temperature is efiected within six hours in nitrogen with 0.2 percent There resulted the following values:

:3900; h/p. =0.3.l0 cm./ka.. at 20 cycles -i /,u. =2.5.l0 T 130 C.; ,,,,=0.915 B /B =0.16

Example 3 Composition:

53.5 mole percent Fe O 30.5 mole percent MnO, and

16.0 mole percent ZnO.

wherein =reversible permeability in the remanence point.

Example 4 Composition:

55.5 mole percent Fe O 36.5 mole percent MnO, and 8.0 mole percent ZnO.

Cores produced in the manner described in connection with the first example exhibited the following characteristic magnetic values:

Example 5 Composition:

52.5 mole percent Fe O 23.5 mole percent MnO, and 24.0 mole percent 2110.

The iron oxide used in this example had a tetra threadlike particle structure. The initial raw materials are constituted so that the end product contains substantially only the impurities noted in percent by weight, namely, 0.02 percent SiO 0.02 percent TiO 0.002 percent A1 0 0.02 percent CaO'. Cores produced as described in the first example are sintered at 1270 C. first for three hours in air and thereafter for twelve hours in nitrogen with an oxygen content of less than 0.02 volume percent, whereupon they are slowly cooled to room temperature, within about ten hours, in nitrogen. The following values were measured:

Further explanations are rendered below with reference to the accompanying drawings.

FIG. 1 shows the hysteresis loop of a magnetic material With isoperm structure;

FIG. 2 represents the three substance diagram with the area or region according to the invention;

FIG. 3 shows the hysteresis loop of an isoperrn ferrite made according to Example 1; and

FIG. 4 shows the course of the reversible permeability of an isoperm ferrite made according to Example 3, in dependence upon the field strength.

It will be seen from FIG. 1 that the central region of both hysteresis loop legs, in a hysteresis loop of a magnetic material with iso perm structure, rises linearly, describing due to its parallelism a parallelogram with a width corresponding to twice the coercive power, the height of the parallelogram corresponding in this case to six times the remanence induction.

The three-substance diagram Fe O -MnO-ZnO, represented in FIG. 2 shows the area provided by the present invention which contains the quantitative composition of the initial oxides employed in the new method. Numerals l, 2 and 3 indicate the corner points for which numerical values are specified in the claims.

In the hysteresis loop of an isoperm ferrite produced according to the Example 1, as shown in FIG. 3, the remanence induction B lies at about 0.75K gauss and the coercive power H at about 0.07 ma./cm.

In FIG. 4, showing the course of the reversible permeability of an isopenm ferrite made according to the Exarnple 3 in dependence upon the field strength, the dash line indicates the course of the reversible permeability extending from the curve which denotes the deinagnetized condition. Also apparent from this figure is the slight error or alignment of the reversible permeability between effective magnetization and demagnetization.

Changes may be made within the scope and spirit of the appended claims which define what is believed to be new and desired to have protected by Letters Patent.

We claim:

1. A method of producing a soft magnetic ferrite with isoperm character upon a basis of iron-manganese-zinc, with an initial permeability of 52000 and a ratio of the remanence induction B to saturation induction B of which does not contain more than a total of about 0.2% by weight of foreign substances, including at the most about 0.03% by weight silicic acid and at the most about 0.03% by weight of any other disturbing foreign substance, the initial substances being intermixed in proportions of mole percentages in a range with the following corner points in a three substance diagram:

(1) 50 mole percent Fe O 24 mole percent MnO 26 mole percent ZnO (2) 52 mole percent Fe O 16 mole percent MnO 32 mole percent ZnO (3) 57.5 mole percent F6203 42.5 mole percent MnO.

comprising the steps of annealing the mixture at temperatures between about 850 and 950 C., thereafter grinding the annealed material, molding to the desired shape, sintering the molded material at temperatures between 1200 C. and 1350 C., and cooling the same in an inert gas atmosphere containing less than about 0.02 volume percent oxygen.

2. A method of producing a soft magnetic ferrite with isoperm character on the basis of iron-manganese-zinc, according to claim 1, comprising the steps, following sintering of the molded material, of initially quickly cooling the same within about 5 to 15 minutes, from the sinter temperature to a temperature between 900 C. and 500 C., in an inert gas atmosphere containing less than 0.5 volume percent oxygen, and thereafter gradually cooling it to room temperature.

3. A method according to claim 1, wherein the final cooling is slowly effected within 12 to 20 hours.

4. A method according to claim 3, wherein the initial substances are intermixed in wet condition.

5. A method according to claim 1, wherein the annealing is efieoted within a short time of about one hour, at about 900 C.

6. A method according to claim 2, wherein the sintering is effected at temperatures between 1240 C. and 1320 C., Within 1 to 15 hours, in an atmosphere selected from the group of air and nitrogen.

7. A method according to claim 2, wherein the molded material is sintered at temperatures between 1200 C. and 1300" C., first for about 3 to 5 hours in air, and thereupon for about 3 to 12 hours in pure nitrogen.

8. A method according to claim 2, wherein the sinter temperature and the sinter duration are so selected, that the density of the ferrite material amounts to more than 4.5 g./Om.

References Cited in the file of this patent UNITED STATES PATENTS 2,636,860 Snoek et a1. Apr. 28, 1953 2,886,529 Guillaud May 12, 1959 2,924,573 Sasaki et al. Feb. 9, 1 960 2,956,024 Maxson Oct. 11, 1960 

1. A METHOD OF PRODUCING A SOFT MAGNETIC FERRITE WITH ISOPERM CHARACTER UPON A BASIS OF IRON-MANGANESE-ZINC, WITH AN INITIAL PERMEABILITY OF US$2000 AND A RATIO OF THE REMANENCE INDUCTION BR TO SATURATION INDUCTION B8 OF 